1. Field of the Invention
This invention relates to a stretch film packaging machine, and more particularly to a packaging machine in which some items such as raw fresh foodstuffs and other foodstuffs sold in a supermarket or a department store, etc. are mounted on a container such as a tray, etc. The container is covered by a stretch film and the film is folded down over the tray, thus packaging the item.
2. Description of the Prior Art
A stretch film packaging machine which has been developed in recent years is constructed such that both the size of the packaging tray and the height of the stored item are automatically sensed and a length of the film to be cut is defined based on the result of this sensing operation. Thus, the mechanism assures positive and superior packaging even if the size of the tray to be packaged is varied. Such a packaging machine as described above is made such that the tray is normally fed into the machine in a direction perpendicular to the film feeding direction.
A machine which does not have the above-noted sensing means and provides for the setting of a specified length of the film to be used has also been made. This construction is employed because there are several trays presently used with different lengths, ranging from long ones to short ones, rather than trays with different widths and the machine aims to have a wide range of trays which can be used and still assure positive and superior packaging. However, in this case, since the film length in the width of the tray is always kept constant as long as the applied film is not changed, the following disadvantages may be found. It is necessary for the feeding conveyor at the in-feed or entrance part of the conventional type of machine to provide intermittent feeding of the packaged item, so that, as shown in FIG. 16, pusher conveyor 1 is applied. This unit is required because the item or tray A properly mounted on the conveyor is transported in synchronism with the vertical movement of elevator head 2 and the delivery of the tray A onto elevator head 2 is performed by the end part of pusher conveyor 1 due to the performance of pusher conveyor 1.
Therefore, when a narrow width tray, such as a tray for storing mackerel pikes is to be packaged, a substantial margin C of the film b remains. This margin C does not cause any problem in a packaging machine (FIGS. 12 to 14) where the feeding-out or exit port 12 is on the same side as the feeding-in or entrance port 11. However, as shown in FIG. 16, in the case of a packaging machine (FIGS. 9 to 11) where the tray exit 12 is placed opposite to the entrance port 11 a problem occurs. As is shown in FIG. 17, folding plate 4 moves the tray A toward exit or feeding-out conveyor 34 when the front part of the film has been folded, which results in that packaging may not be performed in a superior manner, and ultimately, packaging might not be completed at all.
Element 1 in FIG. 16 designates a pusher conveyor. Elevator head 2 is arranged at the feeding-out end or output of pusher conveyor 1, such that elevator head 2 may be moved up and down. Lateral folding plates 3, 3', front folding plate 4, discharging pusher 35 and heating belt 34 are arranged over elevator head 2. When item A is mounted on elevator head 2 by pusher conveyor 1, whereby item A is raised up, additional margin C is produced at the film b near heating belt 34. Therefore, when the film is folded by front folding plate 4, it results in the form as shown in FIG. 17. Due to this arrangement, in the conventional type of the device as above, the kind of tray which may be used and which will still assure a superior packaging is limited.
In order to eliminate the above-mentioned problems, it has been developed to make a packaging machine wherein the width of the tray to be packaged is detected, and the length of movement of the folding plate is controlled in response to the width of the tray. Since the device is constructed such that the mechanical parts are not operated by an electric motor, but by compressed air, the control of the length of movement of the folding plate is relatively simple. Where the mechanical parts are operated by compressed air, a facility for supplying the compressed air such as an air compressor is required, so that the entire unit becomes large in size and heavy in weight. Since the width of the tray is detected and controlled, the control circuit becomes complicated. The processing speed of this type of machine is also restricted.
In the above-noted stretch film packaging machine, the items are packaged with a stretch film. Thereafter the packaged items are transferred onto heating belt 34, the bottom part of the folded stretch film is sealed and at the same time the unit price, weight and price of the items are printed on the label by the label printer and the printed label is adhered or attached to the packaged items. It is necessary to attach the above-noted label at any one of the four corners of the container (item) because attaching the label in the center of the item may cause the customer to have a restricted view of contents of the container.
Random adherence of the label on the container or irregular adherence thereof may not only adversely effect the outer appearance, but also degrade or reduce the value of item, so that careful attention must be paid to the position of the adherence of the label at the supermarket.
The adhering position of the label printer must always be moved each time the size of the item to be packaged is varied. A trial adherence of a label must be done, resulting in quite a troublesome operation.
It has previously been proposed that in the conventional type of packaging machine a weighing device and a label applying device are integrally assembled to adhere the label to the item on the heating belt. However, the label may not be adhered in the same position unless the label adhering position of the label printer is moved in response to the size of the item to be packaged.